03 S10 2.2 L battery problems

Hello, I’ve been having some trouble with my s10 and was wondering if anybody could help me diagnose the cause of the problems. First of all, it’s a 2003 s10 with the 2.2 engine, the truck has about 110,000 miles on her. Several times now i’ve had the problem where I would go to start the truck and when I turned the key from run to start there would be a click and nothing would happen, just one not very loud click. I checked the battery and my battery would be low. The first thing I did was take off the battery terminals (side post) and one of the battery terminals, I don’t remember which anymore, was very corroded. There was a lot of green corrosion on the battery terminal screw. I cleaned the terminal screw off and tightened both cables, jumped the truck, and it drove fine for a couple weeks.

Then after a couple of weeks I stopped at a gas station and the truck wouldn’t start, all the lights came on and there was a dinging noise, just like normal, but when I turned the key to start just a click. When I removed the battery terminal screw it was very corroded again. I cleaned it off as best I could and after getting jumped the truck ran just fine. When I got home I took both the screws out and cleaned them with a bench grinder wire wheel and also cleaned the battery cable end that they go through. The truck was fine for a month or so until I had the same problem. This time there was no green corrosion, just that the screw had formed a coating of rust all over it. Note that this is the same battery terminal that keeps corroding, the other one is fine. I cleaned off the screw and coated both screws and terminals with a dieletric grease to stop it from happening again.

My truck has been running just fine for several weeks now. I use a fm transmitter that plugs into my cigarette lighter and it tells me the voltage of the battery, including the voltage it’s charging at. When I first get into the truck the battery reads a healthy 12.8 volts, and after I start it the battery always reads around 13.8-14.5 volts while it’s charging. The problem now is that this morning when I got into my truck to leave for work, it started just fine, but I noticed my fm transmitter read 11.6 volts. Then I looked at the dash and my battery light was on. I checked the battery with my multi-meter while the truck was still running and it confirmed those numbers. Since I didn’t have time to fool with it before work I took my wife’s vehicle to work.

I’ve been assuming all day that it’s a bad alternator, but when I got home I started the truck and the battery voltage reads fine now. It’s charging at 14.2 volts and the battery lights went out. I drove the truck around my property a bit and shut it off and started it a couple of times with no troubles. I also checked my battery connections and there was no corrosion or rust. What could possibly be causing all of these things to happen? My theory on the original battery not charging correctly problem is that the corroded battery terminal was preventing the battery from charging even though my alternator was putting out the correct voltage, then I would clean the terminal and it would fix the problem until the terminal corroded again. I have no theory on the battery light and not charging this morning, then it working perfectly.

On a side not something else that it also does that is weird; since I don’t know if this is related or not I’m putting it at the bottom. Sometimes when I go to start my truck and turn the key from off to run, everything lights up and works as normal, but when I turn the key from run to start all the dash lights go out and nothing happens, no click or anything. The dash lights go out just like normal when you start the vehicle. When I let go of the key they come back on like normal. Sometimes I don’t have to do anything except to turn the key again and the truck starts up with no problems at all. And sometimes I wiggle the parking lever while turning the key and it’ll eventually start. Could this be a security issue?